package dfs;

/**
 * 二、 二叉树的深搜
 * 4. 验证二叉搜索树
 * 2024-11-16
 */
public class demo9 {
    long prev = Long.MIN_VALUE;
    public boolean isValidBST(TreeNode root) {
        if(root == null) return true;

        boolean left = isValidBST(root.left);
        //剪枝
        if(left == false) return false;
        boolean cur = false;
        if(root.val > prev) {
            cur = true;
        }
        //剪枝
        if(cur == false) return false;

        prev = root.val;
        boolean right = isValidBST(root.right);
        return left && cur && right;
    }
}
